The main purpose of a cellular network, e.g. a digital network using a standardized system such as the Global System for Mobile communications (GSM), the Digital Cellular System (DCS), or the Personal Communication System (PCS) 1900, is to convey a call by radio on a carrier frequency between a base station of the network and a mobile terminal of a user who is a subscriber to the network. Each cellular network is allocated a certain range of frequencies, which range is restricted compared with all of the frequencies that are useable in the system in question. By way of example, GSM has 125 possible carrier frequencies, and, in France, most of them are shared between two main operators, each owning a respective digital cellular network.
Furthermore, the territory covered by any given cellular network is subdivided into cells, each cell generally having a base station suitable for communicating with all of the mobile terminals that are situated in the cell at any given time. A well-known subdivision configuration given by way of example consists in choosing cells that are ideally adjacent, of the same size, and hexagonal in shape. It is thus possible to define a particular set of cells, referred to as a "pattern", e.g. a seven-cell pattern constituted by a central cell surrounded by six adjacent cells.
Moreover, the base stations and the mobile terminals of a cellular network are of limited range, i.e. beyond a certain distance, communication is no longer possible because of the attenuation of the carrier frequency. It is thus possible for the same carrier frequency to be used in different places provided that these places are far enough apart. This is particularly important because, as indicated above, each network possesses only a limited number of carrier frequencies for an ever increasing number of subscribers. Thus, each cellular network defines a scheme for re-using frequencies, and, by way of example, reference may be made to the above-mentioned seven-cell pattern. In such a pattern, different carrier frequencies are allocated to each cell, each cell being allocated one or more carrier frequencies. The pattern is repeated by shifting such that, for any given cell in the initial pattern, there are six closest neighboring cells that reuse the same frequencies, and these cells are uniformly distributed on a circle whose center coincides with the center of the given cell.
The boom in mobile telephones is such that a large and ever-increasing number of private individuals presently possess mobile terminals. Among these users, who are attracted by the concept of being able to communicate with a high degree of freedom, many also have a cordless telephone in their own home or might subsequently procure such a telephone which enables them to be on the phone while being free to move in a zone close to a fixed station in the home, the cordless telephone communicating with said station by radio, the station itself being connected by wire to a wired telecommunications network, e.g. a network of the Public Switched Telephone Network (PSTN) type.